It is well-known that the costs of cabling becomes more and more significant in instrumentation and allied fields. While the costs of signal processing have fallen drastically with the introduction of large scale integrated circuits, the expenses for cabling have not changed too much.
There are several systems known in the art for reducing costs in the case of the digital signal transmission by using standardised interfaces and link systems. However, no similar solution exists for analog signals. Of course, digital transmission can also be used for transmitting of analog messages by using an A-to-D converter at the sending point and D-to-A converter at the destination point. But this method needs additional components and introduces additional conversion errors.
For analog signals, connection methods are still in use, e.g., point-to-point connections, which are very wasteful. Especially in the analog data acquisition field, the costs for the wiring are very high, because between each analog sensor and the corresponding multiplexer input of the central data acquisition unit, individual connections are used. The number of the sensors can be several hundred.
A dominating percentage of sensors, like strain gage and other bridges or resistance temperature detectors, need excitation, which causes additional wiring costs. Moreover, for high accuracy measurement the excitation is regulated. This needs additional sense feedback wires from the bridge to the excitation unit to avoid error through the excitation wire resistance. If the excited sensors are not mounted closely enough together, then even more regulated excitation units with additional wires should be used, namely one separate excitation unit for each sensor group.